Our overall objective is to learn how protein synthesis is regulated in animal tissue culture cells that are transformed by RNA tumor viruses. To accomplish this, however, it will be necessary to study virulent virus infection as well, since this will serve as a useful standard for comparison. Our primary approach will be to develop and purify cell-free protein synthesizing systems which will enable us to study in vitro the mechanisms by which different viruses regulate the synthesis of their own specific proteins, as well as the proteins of the cell which they infect. A major objective will be to obtain such a system from a normal cell line which can be infected or transformed by a wide variety of different viruses, so that the specific effects of each virus on cellular protein synthesis can be compared. A second approach to the problem of protein synthesis regulation will be to compare the different types of RNA produced by various viruses, to determine how structure relates to function. This question will be studied a) by purifying the different forms of RNA and comparing their messenger activities, and b) by direct structural analysis with the electron microscope. We also intend to determine the initiation sequences of various viral RNA's using the purified initiation systems described above (by the method of Steitz and Hindley and Staples).